This invention relates to portable information handling systems, and more particularly to a power switch for an external module adapted to interface with a portable information handling system.
Personal digital assistants (PDAs) allow busy people to perform a variety of tasks while away from a home or office computer. Many models of PDAs can be docked when the user is at his or her computer, allowing the user to recharge the PDA and/or to connect the PDA to the computer. Many PDAs include a slot for the insertion of external cards or modules, such as PCMCIA cards or proprietary modules. For example, the original schemes introduced the PCMCIA slot in notebooks and then moved on to add Cardbus for higher performance. Later, the Visor(copyright) brand PDA manufactured by Handspring, Inc. included a slot for accepting external Springboard(copyright) modules. Such external cards or modules can perform a variety of functions, such as providing additional memory or performing imaging functions. Typically, an external module is designed to activate when inserted into a PDA or similar information handling system.
Bigger notebook and laptop computers operate with power from batteries with substantial energy storage capacity. Present day PDAs, handhelds and some thinner laptops lack this luxury in their intended application environment. As these devices get faster, then their processors and associated circuitry will consume more of the internal power resources, thus increasingly limiting the power available for external modules. However, external modules for connection to those PDAs, handhelds and laptops increasingly provide greater functionality, at the price of increased power consumption. Thus, the internal power consumption of a portable information handling system, combined with the power consumption of an external module, can quickly drain the internal power supply of the portable information handling system, if enough power is even available to operate the external module in addition to the portable information handling system.
A switch for an external module adapted for insertion into a portable information handling system switches on a module insertion detection signal when external power is applied. The switch can be located in either the portable information handling system or the external module. In this way, power provided to an external module with high power consumption is accommodated and controlled.
In one aspect of the invention, the application of external power to an external module connected to a portable information handling system switches on a card detection signal, thereby allowing the portable information handling system to detect and activate the external module. Automatic detection and activation of the external module simplifies the use of that external module and allows for easier operation of the portable information handling system in combination with the external module.
In another aspect of the invention, when external power is disconnected from the external module, the card detection signal is switched off, thereby deactivating the external module and electrically disconnecting the external module from the portable information handling system. In this way, the external module does not demand power when the portable information handling system is not connected to an external power source, conserving power within the portable information handling system and extending its operating time.
In another aspect of the invention, power is provided to an external module before it is logically connected to the portable information handling system. Once the external module is plugged in, it is recognized and configured, and becomes operational. A protocol allows for an orderly transition of context when an external module is inserted into the portable information handling system, so that it does not drain the internal power of the portable information handling system. Similarly, when the external module is disconnected the portable information handling system continues to function without any interruption.
In another aspect of the invention, substantially all of the power for the external module is provided independently from the internal power supply of the portable information handling system. In this way, the portable information handling system can use a power source at any voltage (e.g., 5V, 3.3V, 1.8V or other voltages) regardless of the voltage needs of the external module. Similar freedom is also accorded to the external module, which can be designed to run on any voltage. The portable information handling system handles exception events, such as external module insertion, without external power. Thus, only a small fraction of the power utilized by the external module is provided by the internal power supply of the portable information handling system (e.g., on the order of 2-5 mA).
The invention will be more fully understood upon consideration of the detailed description that follows, taken together with the accompanying drawings.